Why are homosexual relationships (between a man and a man, or a woman and a woman) forbidden, even in the absence of health harms?

The Shari'ah has forbidden sodomy between men and lesbianism between women. This is the act of the people of Lot, due to its great repulsiveness and immense harm. This is because legal rulings are issued from Allah's all-encompassing knowledge of everything. Thus, everything forbidden by the Shari'ah contains either pure harm or predominant harm. It has been scientifically proven that these relationships cause diseases such as AIDS, and they also contradict sound human nature (fitra).